PROJECT SUMMARY Mass incarceration has been hypothesized to be a major driver of HIV acquisition for heterosexual, African American women. Incarceration can increase engagement in HIV risk behaviors (including concurrent sexual partnerships, transactional sex, and condomless sex) for both the incarcerated person and their sexual partners and inmates are approximately five times as likely to be HIV-infected compared to the general population. However, it is not known how mass incarceration impacts HIV transmission and prevalence at the population-level. The objectives of the proposed study are: 1) to estimate the proportion of HIV transmission events among African American women attributable to a male sexual partner?s incarceration using the city of Philadelphia as a case study; and 2) to determine the effectiveness of treatment as prevention (TasP) and pre- exposure prophylaxis (PrEP) prescription strategies for heterosexual couples with a history of incarceration under selected assumptions (i.e. HIV viral load, number of partners) in preventing transmission attributable to incarceration. Using a novel complex systems approach known as agent-based modeling, a population-based model will simulate HIV transmission month-to-month in a dynamic, sexual-contact network representing African American heterosexual men and women at high-risk of HIV living in the city of Philadelphia from 2005-2015. In order to estimate the proportion of HIV transmission events attributable to incarceration, the following will be calculated: 1) the number of HIV incident, prevalent, and mortality cases; 2) HIV incidence rates among all women and those with an incarcerated male partner; and 3) the percentage increase in HIV incidence, prevalence, and mortality attributable to a one unit increase in the rate of incarceration. The effectiveness of hypothetical prevention scenarios (i.e., PrEP prescription for all serodiscordant couples) during each epidemic phase will be estimated by the fraction of new HIV infections averted over pre-specified intervals (e.g., 2, 5, and 10-year time horizons). The model will be based on surveillance data collected by the Philadelphia Department of Public Health as well as empirical literature regarding HIV risk behaviors associated with a history of incarceration. Extensive model calibration and validation procedures will be conducted to test robustness and ensure goodness of fit. This study will be the first to estimate the proportion of HIV transmission events among African American women attributable to mass incarceration and identify strategies that maximize reductions in HIV transmission due to incarceration at the community level. The results of this project pave the way for targeted prevention by identifying women at highest risk of HIV acquisition and what intervention strategies are most effective in decreasing overall HIV incidence in an urban, U.S. setting.